The present invention relates to inflow regulation in a production pipe with a lower drainage pipe for production of oil or gas from a well in an oil- and/or gas reservoir. The invention comprises adjustable throttling or valve devices in conjunction with openings in the drainage pipe, providing that the inflow to the drainage pipe may be controlled according to the pressure profile of the reservoir. Thus, the invention is in particular very suitable for long horizontal wells in thin oil zones with high permeability in the geological formation.
From U.S. Pat. Nos. 4,821,801, 4,858,691, 4,577,691 and GB patent publication No. 2,169,018, there are known devices for recovery of oil and gas from long horizontal and vertical wells.
These known devices comprise a perforated drainage pipe with, for example, a filter for control of a sand around the pipe. A considerable disadvantage of the known devices for oil and/or gas production in highly permeable geological formations is that the pressure in the drainage pipe increases exponentially in the upstream direction as a result of the flow friction in the pipe. Because the differential pressure between the reservoir and the drainage pipe will decrease upstream as a result, the quantity of oil and/or gas flowing from the reservoir into the drainage pipe will decrease correspondingly. The total oil and/or gas produced by this means will therefore be low. With thin oil zones and highly permeable geological formations, there is a high risk of coning, i.e. a flow of unwanted water or gas into the drainage pipe downstream, where the velocity of the oil flow from the reservoir to the pipe is highest.
The applicant's own EP-patent publication No. 0,588,421 discloses a production pipe for production of oil or gas from an oil or gas reservoir where a lower part of the pipe comprises a drainage pipe divided into a number of sections with one or more inflow-restriction devices that control the inflow of oil or gas from the reservoir to the drainage pipe on the basis of anticipated loss of pressure along the drainage pipe, the reservoir's anticipated productivity profile, and the anticipated inflow of gas or water.
The patent publication mentioned above discloses one embodiment of an inflow-restriction device, where a thickening in the form of a sleeve or gate is provided with one or more inflow channels, and where the inflow may be regulated by means of one or more screw or plug devices. By using short or long screws which extend into the channels. the flow-resistance in the channels can be varied. A further embodiment suggests to providing the drainage pipe with passing slots or holes and arranging a surrounding sleeve, which is movable in the lengthwise direction, at each section of the drainage pipe.
The above mentioned technology sustains satisfactory possibilities for the regulation of the inflow in the individual sections of the drainage pipe. Meanwhile, as the pipe has been installed in the reservoir, it has been experienced that a precise adjustment of the inflow at each section by the use of remote controlled means, such as coiled tubing or such as a well tractor tool, has been quite comprehensive and time consuming. Further, the inflow-restriction means described represent quite complex designs, that will require comprehensive and expensive machining operations in the manufacture of such inflow-restriction means.